Select List değiştiğinde olay tetikleme
<select id="mySelect" onchange="myFunction()">
<option value="Audi">Audi</option>
<option value="BMW">BMW</option>
<option value="Mercedes">Mercedes</option>
<option value="Volvo">Volvo</option>
</select>
Javascript Kodu
<script>
function myFunction()
{
var x = document.getElementById("mySelect").value;
document.getElementById("demo").innerHTML = "You selected: " + x;
}
</script>